Known semiconductor voltaic cells for the generation of electrical energy using a radioactive energy source suffer from several disadvantages, including a relatively low voltage output, relatively low power output and a relatively short life. These disadvantages are caused largely by the failure to efficiently harness the energy of the charge carriers (electrons and holes) when they are excited into higher energy levels by collisions with the energetic particles (e.g., alpha particles, beta particles) released during decay of the radioactive energy source. Although the charge carrier collisions create electrons in the conduction band and corresponding holes in the valence band, it is customary to describe only the electrons, it being understood that the same processes that affect the electrons also affect the holes. The excited carriers may lose energy through inelastic collisions, such as phonon excitation of the semiconductor lattice, they may recombine, or they may be captured by the radioactive decay products (such as defects produced when tritium decays) which accumulate in the semiconductor lattice as the cell ages. The voltage, power, and life of such cells could be increased by collecting the excited carriers while they are in the energy bands above the conduction band and before they lose significant kinetic energy through collisions, recombine or are captured by radioactive decay products.